1. Field of the Invention
This invention relates to a communication apparatus which communicates a signal, and in particular, relates to a communication apparatus which realizes effective automatic power control (APC).
2. Description of the Relevant Art
A first background technology will be described.
Meanwhile, a matter, which will be described here, does not necessarily mean that every technologies are conventional technologies.
FIG. 6 shows a configuration example of a wireless communication apparatus which adopted an one channel (ch) APC system.
The wireless communication apparatus in this example is equipped with an input terminal 61, a variable amplifier 62, a power amplifier (PA) 63, a filter 64, an antenna 65, a directional coupler 66, a wave detector 67, a comparator 68, and a loop filter 69.
In the wireless communication apparatus of this example, power detection is carried out at the antenna 65 end, to carry out APC.
FIG. 7 shows a configuration example of a wireless communication apparatus in such a case that 4ch APC is carried out by use of the configuration shown in FIG. 6, and schematically, four pieces of the configurations shown in FIG. 6 are disposed in parallel.
Concretely speaking, the wireless communication apparatus in this example is equipped with four pieces of input terminals 71a to 71d, four pieces of variable amplifiers 72a to 72d, four pieces of power amplifiers (PA) 73a to 73d, four pieces of directional couplers 74a to 74d, four pieces of wave detectors 75a to 75d, a control section 76, four pieces of variable filters 77a to 77d, a coupling circuit (series resonant circuit) having four sets of coils 80a˜80d and capacitors 81a˜81d, and an antenna 79.
Meanwhile, in this specification, a component part of the variable filter having a coupling circuit for a plurality of channels (in this example, 4ch) is called as antenna sharing, device.
In the wireless communication apparatus of this example, power detection is carried out in a final stage of the power amplifiers 73a to 73d which are a previous stage of the antenna sharing device (in this example, the variable filters 77a to 77d and the coupling circuit 78). Meanwhile, one antenna 79 is shared by a plurality of high frequency channels under the control of the antenna sharing device, and therefore, it is impossible to carry out power detection at the antenna 79 end. In addition, the control section 76 carries out such feedback control that transmission levels are compared and then, output correction is carried out, independently as to 4ch.
However, in the wireless communication apparatus shown in FIG. 7, there are problems as follows.
That is, in the antenna sharing device, minimum elongation frequency between respective channels becomes necessary, and when elongation frequency is insufficient, an impedance of another channel does not become infinitely great (open), and therefore, transmission power leaks to another channel through the coupling circuit 78, and a transmission loss fluctuates. In sum, a transmission loss of the antenna sharing device fluctuates, due to elongation frequency of each channel.
Then, in case that a transmission fluctuates due to setup frequency of the antenna sharing device, the antenna sharing device exists outside an APC loop, and therefore, in order to absorb fluctuation of the transmission loss of the antenna sharing device, some sort of correction becomes necessary. For example, conceivable is a method for carrying out output correction depending on elongation frequency, but this requires a device for monitoring frequency of all channels, and therefore, a device cost increases, which is not preferable.
In this manner, in the APC system shown in FIG. 7, there is such a problem that transmission power of each channel at the antenna 79 end fluctuates due to setup frequency of the antenna sharing device, and stable power control is impossible.
A second background technology will be described.
Meanwhile, a matter, which will be described here, does not necessarily mean that every technologies are conventional technologies.
FIG. 8 shows a configuration example of a wireless communication apparatus having an APC circuit which used a heat wave detector.
A wireless communication apparatus in this example is equipped with a modulating signal generator 91, a voltage-controlled gain controller 92, a power amplifier (PA) 93, a directional coupler 94, a heat wave detector 95, a differential amplifier 96, and an integrator 97.
The wireless communication apparatus in this example adopts an APC system by use of the heat wave detector 95, and uses the wave detector (heat wave detector) 95 which converts high frequency power into heat to carry out power measurement, and therefore, a wave detection level is not swayed by a wave form of modulation.
However, it takes time until a wave detection level becomes stable, and therefore, there is such a problem that it is not adequate to the APC loop which is locked at high speed.
In addition, FIG. 9 shows a configuration example of a wireless communication apparatus having an APC circuit which used a modulation correction coefficient.
The wireless communication apparatus in this example is equipped with a modulating signal generator 101, a voltage-controlled gain controller 102, a power amplifier (PA) 103, a directional coupler 104, a logarithmic amplifier (wave detector) 105, a reference voltage source 106, a differential amplifier 107, and an integrator 108.
The wireless communication apparatus in this example adopts the APC system by use of a modulation correction coefficient, and uses the logarithmic amplifier 105 as a wave detector, and therefore, there is no need to consider such time that a wave detection level becomes stable, like the configuration shown in FIG. 8.
However, a wave detection level changes due to a modulation wave form, and therefore, there is such a problem that there is a necessity to change a reference voltage of APC (output voltage from the reference voltage source 106) in tune with a type of modulation, by disposing a correction coefficient with respect to each type of modulation (modulation system). In addition, there is a limit in the number of correction coefficients, and therefore, there is a limit in types of modulations for which APC is available, and on this account, for example, there is such a problem that it becomes impossible to control even if the number of types of modulations increases in the future. In addition, in order to setup the correction coefficient, conceivable is such a configuration that, for example, a resistor volume and a ROM (Read Only Memory) table etc. are used, but there is such a problem that it is directly linked to cost rise. In addition, as to which type of modulation responsive signal is outputted, an instruction signal from the modulating signal generator 101 becomes necessary, and therefore, there is such a problem that control becomes complex.
[Patent Document 1] JP-A-2000-22581 publication
As shown in the above-described first background technology and the above-described second background technology, development of a communication apparatus which realizes effective automatic power control (APC) has been requested.
Concretely speaking, as shown in the above-described first background technology, development of such a communication apparatus that, for example, even in case that transmission power of each channel at the antenna end fluctuates due to setup frequency of the antenna sharing device, stable power control is possible, has been requested.
In addition, as shown in the above-described second background technology, development of such a communication apparatus that, for example, it does not take so much time until a wave detection level becomes stable, and it is applicable to the APC loop which is locked at high speed, and in addition, a wave detection level does not change due to a modulation wave form, and there is no need to change the APC reference voltage in tune with a type of modulation, has been requested.
The invention is a thing which was made in view of the suchlike conventional circumstances, and aims to provide a communication apparatus which realizes effective automatic power control (APC).
Concretely speaking, an object is to provide such a communication apparatus that, for example, even in case that transmission power of each channel at an antenna end fluctuates due to setup frequency of an antenna sharing device, stable power control is possible.
In addition, an object is to provide such a communication apparatus that, for example, it does not take so much time until a wave detection level becomes stable, and it is applicable to an APC loop which is locked at high speed, and in addition, there is no need to change a reference voltage of APC in tune with a type of modulation.